Anhydrite mine driller at work preparing hole for blasting charge. ICI in Billingham. 
Picture Stockton Archive
A Pictorial History of Stockton-on-Tees
Anhydrite mine driller at work preparing hole for blasting charge. ICI in Billingham.
The Mine entrance is located inside the site North of Haverton hill road and east of Belasis Av on waste land behind the Council Incinerater. I will send in picture of entrance as it is today -capped off
With only 6 months of knowledge whilst working at ICI I would say that the entrance to the Anhydrite Mine was on the same road inside the works that led to the Sulphuric Acid Plant. The Sulphuric Acid Plant overlooked the houses on Belasis Avenue so I would say you are right Stan about the location of the entrance to the Mine.
From memory the entrance to the Anhydrite mine at Billingham, now “capped off” was in the ICI complex not far from the junction of Belasis Avenue and Greenwood Road. The boundaries of the mine extended about one mile east to west and two miles north to south. In 1984 during the battle with NIREX to stop it being used as a nuclear dump the Northern Echo published a fairly detailed map of the boundaries of the mine. Two thirds of the working were claimed to be under the factory complex while the rest extended north under parts of Billingham, mainly under the houses on the Cowpen Lane estate, with one section reaching almost to Low Grange Avenue along Marsh House Avenue and parts of the Cowpen Industrial estate. At its most easterly point it crossed the Cowpen Bewley Road between Cowpen Bewley village and Haverton Hill reaching almost to the Seal Sands Road. I can vouch personally of its existence under the Cowpen Lane estate having heard the shot firers doing their job regularly when I lived there.
Can anyone tell me where about the anhydrite mine entrance is located and under which parts of Billingham does it run?
The mine is still under Billingham and District , now “Capped-Off ” I also visited the mine and was amazed at the traffic below ground tractors ,dumpers and wagons and the facilities such as canteen and medical support. On a still night it was possible a to feel the blasting tremor on the surface. It became National News in the 1980s when British Nuclear Fuels wanted to store its waste in the caverns, this raised a storm of objections and the forming of Billingham Against Nuclear Dumping (B.A.N.D.), which saw thousands taking to the streets in protest
My first job on leaving school at fifteen was as a messanger Boy at Billingam ICI, we were given a trip down the anhydrite mine and were surprised to discover how large the operation was, the mine had roads underground that could take a double decker bus, trucks and other mobile equipment could drive around the mine. I would expect the mine is still there, I could not imagne them filling it in when mining finished. I vividly remember air locks on the roads as you travelled along them.